Breathing assistance apparatus

ABSTRACT

In one embodiment, a nasal cannula is shaped to fit within a user&#39;s nares, where the nasal cannula includes at least one prong allowing high flow delivery of humidified gases and creates positive airway pressure in the patient&#39;s airway. The prongs have angled ends such that, in use, gases flowing through the prongs are directed to the user&#39;s nasal passages. The nasal cannula body is partially swivelling and preferably has a ball joint connector. In another embodiment the nasal cannula may have at least one flared end prong that preferably seals within a patient&#39;s nare.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference and made a part of the present disclosure.

BACKGROUND Field

The present invention relates to apparatus for treating sleep apnea. More specifically, the present invention provides a nasal positive airway pressure device.

Description of Related Art

Obstructive Sleep Apnea (OSA) is a sleep disorder that affects up to at least 5% of the population in which muscles that normally hold the airway open relax and ultimately collapse, sealing the airway. The sleep pattern of an OSA sufferer is characterised by repeated sequences of snoring, breathing difficulty, lack of breathing, waking with a start and then returning to sleep. Often, the sufferer is unaware of this pattern occurring. Sufferers of OSA usually experience daytime drowsiness and irritability due to a lack of good continuous sleep.

In an effort to treat OSA sufferers, a technique known as Continuous Positive Airway Pressure (CPAP) was devised. A CPAP device consists of a gases supply (or blower) with a conduit connected to supply pressurised gases to a patient, usually through a nasal mask. The pressurised air supplied to the patient effectively assists the muscles to keep the patient's airway open, eliminating the typical OSA sleep pattern.

The procedure for administering CPAP treatment has been well documented in both the technical and patent literature. Briefly stated, CPAP treatment acts as a pneumatic splint of the airway by the provision of a positive pressure, usually in the range 4 to 20 cm H.sub.2O. The air is supplied to the airway by a motor driven blower whose outlet passes via an air delivery hose to a nose (or nose and/or mouth) mask sealingly engaged to a patient's face by means of a harness or other headgear. An exhaust port is provided in the delivery tube proximate to the mask. More sophisticated forms of positive airway pressure devices, such as bi-level devices and auto-titrating devices, are described in U.S. Pat. No. 5,148,802 of Respironics, Inc. and U.S. Pat. No. 5,245,995 of Rescare Limited, respectively.

U.S. Pat. No. 5,477,852 of Airways Ltd, Inc. discloses a nasal positive airway pressure device that has a pair of nasal members each having a cannula tip to be inserted into the nares of the patient. Each cannula is tapered from a substantially circular cross-section outside the patient's nostril to a substantially oval cross-section at the tip inserted into the nostril. An inflatable cuff surrounds each, cannula with the interior space of the cuff communicating with the lumen of the cannula through at least one aperture in the sidewall of the cannula. The nasal members are connected to one or more flexible hoses that, in turn, are connected to a source of positive air pressure. In use, positive air pressure is supplied to each cannula tip through the air hoses and nasal members. The positive air pressure inflates the cuffs to hold the nasal members in place and to effect treatment. The nasal device of U.S. Pat. No. 5,477,852 is attached to headgear that is located about a patient's head; this headgear could be considered by many patients as cumbersome and uncomfortable.

Conventional nasal masks used for administrating CPAP treatment are also considered uncomfortable and cumbersome, and prior art nasal masks and the like are noisy (due to air leaks). These disadvantages in many cases are a formidable obstacle to patient acceptance of such treatment. Therefore, a substantial number of patients either cannot tolerate treatment or choose to forego treatment. It is believed a substantial number of such patients could benefit from a nasal positive airway pressure apparatus that is more convenient to use and comfortable to wear, thereby resulting in increased treatment compliance.

As oxygen is supplied as a dry gas it is well known in the art to either heat and/or humidify gases before delivering them for breathing by a patient. In particular when delivering oxygen, or oxygen, or air mixture, it has proven beneficial to humidify the gases first. In WO01/41854 of Vapotherm, Inc. a system is disclosed that allows the delivery of humidified, oxygen through a nasal cannula. This system uses a narrow bore conduit and nasal cannula with, a high resistance to gas flows, thereby requiring the oxygen be of a high pressure. Air, as well as oxygen can also be passed down the conduit and nasal cannula and it too must be of a high pressure. This system allows the delivery of high flows of oxygen enriched air to the patient, but is limited in the flows achievable due to the narrow bore of the cannula resulting in high resistance gas flow and excessive velocity and noise upon exiting the cannula. Furthermore, the narrowness of the nasal cannula in this system allows easy expiration of gases between the prongs and nares and therefore does not create any positive airway pressure.

Innomed Technologies, Inc. manufactures a nasal cannula device called the NASALAIRE™. In this device air or oxygen travels down a wide bore conduit to nasal cannula. The NASALAIRE™ creates a physical seal between the nares and itself, and relies on the absence of leaks around itself and the nares to deliver pressure supplied by a continuous positive airway pressure (CPAP) blower to the airway of the wearer.

SUMMARY

It is an object of the present invention to provide a breathing assistance apparatus which goes someway to overcoming the above mentioned disadvantages or which will at least provide the public a useful choice.

Accordingly in a first aspect the present invention consists in a breathing assistance apparatus comprising:

-   -   nasal cannula, shaped to fit within a user's nares, and adapted         to deliver said humidified gases to said user,     -   a pressurised source of gases,     -   transportation means adapted to, in use, be in fluid         communication with said source of gases and said nasal cannula         and adapted to in use convey said gases to said user,     -   wherein said nasal cannula including at least one prong allowing         high flow delivery of said humidified gases and creating a         positive airway pressure in said patient's airway, said at least         one prong having an angled end, such that in use, gases flowing         through said prong are directed to said user's nasal passages.

In a second aspect the present invention consists in a breathing assistance apparatus comprising:

-   -   nasal cannula, shaped to fit within a user's nares,     -   a pressurised source of gases,     -   transportation means adapted to, in use, be in fluid         communication with said source of gases and said nasal cannula         and adapted to in use convey said gases to said user,     -   wherein said nasal cannula are adapted to deliver said         humidified gases to said user, said nasal cannula including at         least one prong allowing high flow delivery of said humidified         gases and creating positive airway pressure in said patient's         airway, said at least one prong having an end that is flared         outwardly.

To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred forms of the present invention will now be described with reference to the accompanying drawings.

FIG. 1 is a block diagram of a system providing humidified continuous positive airway pressure to a user as might be used in conjunction with a nasal cannula of the present invention.

FIG. 2 is a perspective view of a first embodiment of the nasal cannula of the present invention.

FIG. 3 is a side view of the nasal cannula of FIG. 2.

FIG. 4 is a plan view of the nasal cannula of FIG. 2.

FIG. 5 is a prong end view of the nasal cannula of FIG. 2

FIG. 6 is an exploded view of the nasal cannula of FIG. 2.

FIG. 7 is a side view of a second embodiment of a nasal cannula of the present invention.

FIG. 8 is a side view of a third embodiment of a nasal cannula of the present invention.

FIG. 9 is a perspective view of a fourth embodiment of a nasal cannula of the present invention.

FIG. 10 is a side view of the nasal cannula of FIG. 9.

FIG. 11 is an exploded perspective view of the nasal cannula of FIG. 9.

FIG. 12 is a front view of the prongs of the nasal cannula of FIG. 9.

FIG. 13 is an exploded side view of the nasal cannula of FIG. 9.

FIG. 14 is a side cross-sectional view of a fifth embodiment of the nasal cannula of the present invention where the connection between a body part and connector of the cannula includes a plurality of channels.

FIG. 15 is a cross-section through AA of the nasal cannula of FIG. 14.

FIG. 16 is a side cross-sectional view of a sixth embodiment of the nasal cannula of the present invention including a shield that protects an outlet vent from inlet gases.

FIG. 17 is a cross-section through BB of the nasal cannula of FIG. 16.

DETAILED DESCRIPTION

Whether used in a hospital environment or in a home environment, the nasal cannula of the present invention will generally have associated three main pieces of apparatus. Firstly, an active humidifier, which that controls the temperature of a heater plate heating a body of water to achieve a desired temperature and humidity of the gases being humidified. Secondly, a transport conduit from the humidifier to the patient is also required, which is preferably heated to reduce condensation, or “rain out”. Thirdly, a cannula designed to fit into the nasal cavity and deliver humidified, pressurized gases. In particular, in one embodiment the nasal cannula of the present invention has two flared end prongs that seal within a patient's nares, although in some embodiments the cannula may have a single prong. The cannula prongs are shaped such that a step is created between them so that the prongs abut the user's nasal septum in use. Furthermore, the gripping action of the sides of the prongs to the user's septum in use prevents the prongs from dislodging from the user's nares. In another embodiment the prongs of the nasal cannula are angled toward one another as well as having an angled profile at the outlet of gases, such that gases flow from the prongs flows back into the nasal passage and is not forced up into the rest of the nasal cavity.

With reference to FIG. 1 a humidified Continuous Positive Airway Pressure (CPAP) system is shown in which a patient 1 is receiving humidified and pressurised gases through the nasal cannula 2 of the present invention. The cannula 2 is connected to a humidified gases transportation pathway or inspiratory conduit 3. It should be understood that delivery systems could also be VPAP (Variable Positive Airway Pressure) and BiPAP (Bi-level Positive Airway Pressure) or numerous other forms of respiratory therapy. Inspiratory conduit 3 is connected to the outlet 4 of a humidification chamber 5 that contains a volume of water 6. The inspiratory conduit 3 may contain heating means or heater wires (not shown) which heat the walls of the conduit to reduce condensation of humidified gases within the conduit. The humidification chamber 6 is preferably formed from a plastics material and may have a highly heat conductive base (for example an aluminium base) which is in direct contact with a heater plate 7 of humidifier 8. The humidifier 8 is provided with control means or electronic controller 9 that may comprise a microprocessor based controller executing computer software commands stored in associated memory.

The controller 9 receives input from sources such as user input means or dial 10 through which a user of the device may, for example, set a predetermined required value (preset value) of humidity or temperature of the gases supplied to patient 1. The controller may also receive input from other sources; for example, temperature and/or flow velocity sensors 11 and 12 through connector 13 and heater plate temperature sensor 14. In response to the user set humidity or temperature value input via dial 10 and the other inputs, controller 9 determines when (or to what level) to energise heater plate 7 to heat the water 6 within humidification chamber 5. A flow of gases (for example air) is provided to the chamber through inlet 16 from a gases supply means or blower 15. As the volume of water 6 within humidification chamber 5 is heated, water vapour begins to fill the volume of the chamber above the water's surface and is passed out of the humidification, chamber 5 through outlet 4. Exhaled gases from the patient's mouth are passed directly to ambient surroundings in FIG. 1.

The blower 15 is provided with variable pressure regulating means or a variable speed fan 20 which draws air or other gases through the blower inlet 17 The speed of the variable speed fan 20 is controlled by the electronic controller 18 (or alternatively the function of the controller 18 could carried out by the controller 9) in response to inputs from the controller 9 and a user set predetermined required value (preset value) of pressure or fan speed via the dial 19.

Flared Prong Nasal Cannula

A first embodiment of a nasal cannula of the present invention is shown in detail in FIGS. 2 to 6. Referring to FIGS. 2 and 6, the nasal cannula 2 comprises three main components; the prong part 21, body part 22 and ball connector 23.

The prong part 21 has two nasal prongs 24, 25, each of which are substantially shaped to follow the contours of the human nares and in use are placed inside a user's nares. The prongs 24, 25 extend out from a hollow tubular body 26 that in use fits to the body part 22. Each of the prongs 24, 25 are integrally moulded with the tubular body 26 in a flexible plastics material or grubber, such as silicone, other thermoset elastomers or thermoplastic elastomers such as Kraton™. The prongs 24, 25 are substantially oval tubular members that allow for a passage of gases. In particular, as shown in FIG. 5, the prongs are oval in shape and angled in the same manner as a human's nares. The prongs 24, 25 are angled toward one another (or toward the vertical axis Y) at the top 27, 28 of the prongs and away from one another at the bottom 29, 30 of the prongs. Furthermore, the ends 31, 32 of the prongs flare outwardly and preferably are formed such that the ends of the prongs are thinner in cross-section than the rest of the prongs. The flared thinner section ends 31, 32 of the prongs assist with the sealing of the prongs 24, 25 in use within the user's nares. When in use and with gases flowing through the prongs the force of the gas pressure will force the prong ends 31, 32 to flare outwardly and seal against the inside of the user's nares.

The prongs 24, 25 each include a step 33, 34 formed along their lengths. Each of the steps 33, 34 are formed on the prongs 24, 25 in an opposing manner such that in use, when the prongs are within a user's nares the steps 33, 34 abut the user's nasal septum and form a ledge that prevents dislodgement of the prongs. The prongs 24, 25 also have protrusions 35, 36 formed on their outer edges that abut the sides of the user's nares (opposite to the nasal septum). The protrusions 35, 36 assist in preventing the dislodgement of the prongs, especially if the user moves his or her head. The protrusions 35, 36 also maintain the prongs within the user's nares in a correct orientation such that in use gases flow through the prongs and directly up the user's nasal passages.

The body part 22 is a tubular passageway in which the prong part 21 is connected at one end and a ball joint 37 at the other end. The ball joint 37 extends from the connector 23 and slots into a complementary shaped (partial sphere) socket end 39. The body part 22 also has a number of apertures 38 formed in it, which act as a bias flow outlet vent. Therefore, any gases exhaled by the user through their nose will exit through the apertures 38.

The connector 23 is preferably connected to the inspiratory conduit 3 (see FIG. 1) that supplies gases flow to the cannula 2. The inspiratory conduit 3 may be moulded directly to the connector 23 or other connection mechanisms may be used, such as a friction fit formed between the connector and conduit.

Although a ball and socket joint, as described above, between the body part 22 and connector 23 is preferred other connections may be utilised, such as a flexible piece of silicone, or other appropriate connection. The connection between, the cannula body and connector must be able to be flexed or rotated to allow for the inspiratory conduit 3 to be moved without causing the dislodgement of the nasal cannula 2 from the user's nares.

In the preferred form of the nasal cannula 2 of the present invention the body part 22 and connector 23 are preferably made from a hard or rigid plastics material, such as polypropylene, polycarbonate or acetyl. In other forms the body part 22 and connector 23 may be of different plastics materials to allow for increased slidability between these parts.

The prong part 21 may be supplied in various different sizes such that different sized user's may remove an existing prong part and simply attach a different sized flexible plastics prong part over the body part 22.

To provide additional comfort for the user or ensure the nasal cannula of the present invention do not fall from a user's nares, the nasal cannula may be used in combination with a headgear strap, which in one embodiment is a small flexible tube. For example, FIG. 1 shows a headgear strap 40 extending from the nasal cannula 2. The ends of the headgear strap that attach to the cannula may attach to extensions (or loops) 41 on the body part 22 of the cannula shown in FIG. 2, or may attach about other appropriate areas of the cannula, for example, about the connector 23.

The abovementioned embodiment of the nasal cannula 2 of the present invention is preferably a wide bore pronged cannula used for high flow conditions.

A second embodiment of the present invention is shown in FIG. 7. In this embodiment of the nasal cannula 42 the prongs 43, 44 are preferably small bore prongs for use with lower flow conditions. The prongs 43, 44 are similarly shaped to the prongs 24, 25 detailed above, but may not seal in the same manner as the abovementioned prongs due to the smaller size of the prongs. In fact these prongs may not seal at all in use within the user's nares.

Furthermore, in this second embodiment the nasal cannula 42 is smaller and weighs less as it is only comprised of a prong body 45 and prongs 43, 44, where the body 45 is connected to a small tube that is formed with corrugations or bellows 48 that connect to an inspiratory tube or conduit 47 (similar to the inspiratory conduit 3 described above) that receives a supply of gases.

The corrugations of bellows 48 will bend or move when a weight or force is placed on, the cannula, thereby preventing dislodgement of the cannula 42 from a user's face in use. In particular, the corrugations or bellows 48 prevent transferral of the torque onto the cannula 42 when a user moves his or her head.

The body 45 of the cannula 42 is provided with a number of apertures 46 that allows for gases exhaled by the users to be expelled into the ambient air.

The prong body and prongs of this embodiment of the cannula of the present invention are preferably formed a flexible plastics material or rubber, such as silicone, other thermoset elastomers or thermoplastic elastomers such as Kraton™.

A third embodiment of the nasal cannula of the present invention is shown in FIG. 8 where the cannula may be provided with corrugated or baffled sections on the prongs. The nasal cannula 49 of this embodiment is similar to that of FIG. 2 but the prongs 50, 51 have a series of corrugations 52, 53 formed in them. The corrugations 52, 53 allow for movement of each of the prongs 50, 51 for a better user fit, and allow for movement of the cannula 49 without causing dislodgement of the prongs from the user's nares.

Angled Prong Nasal Cannula

A fourth embodiment of the nasal cannula of the present invention is shown in FIGS. 9 to 13. The nasal cannula 60 has a similar construction to the nasal cannula of FIG. 2 and comprises three main components; a prong part 61, body part 62 and ball jointed connector 63.

The prong part 61 preferably has two nasal prongs 64, 65, each of which are substantially shaped to follow the contours of the human nares and in use are placed inside a user's nares. In some forms a cannula with only one prong may be provided. The prongs 64, 65 extend out from a hollow tubular body 66 that in use fits to the body part 62, preferably about an extension 67 (as shown in the exploded view of the nasal cannula of FIG. 11). Each of the prongs 64, 65 are integrally moulded with the tubular body 66 in a flexible plastics material or rubber, such as silicone, other thermoset elastomers or thermoplastic elastomers, such as Kraton™. The prongs 64, 65 are substantially oval tubular members that allow for a passage of gases.

In particular, as shown in FIG. 12, the prongs are oval in shape (to reflect the shape of human nares) and angled in the same manner as a human's nares. The prongs 64, 65 are angled toward one another (or toward the horizontal axis X) such that angles α are formed between the midlines m, n through each respective prong 64, 65. The angled profile of the prongs 64, 65 means that they are more ergonomically correct with a human's nares and may assist in directing the gases flow from the prongs to the user's nasal cavities. The prongs 64, 65 are constructed such that their cross-sectional width narrows closer to the tip of each prong.

In the preferred form the prongs 64, 65 have an angled and profiled end 76 (see FIG. 10). The angled ends 76 assist in directing gases flow to the user's nasal passages.

Each of the prongs 64, 65 has a flange 73, 74 disposed about its circumference. The flanges 73, 74 are at a position on the prongs 64, 65 such that the each of the flanges rests against the outside of each of the patient's nares. The flanges 73, 74 do not extend inside the nares, but rest at the entranceway of the user's nares, and preferably seal the nares. In some users the flanges 73, 74 may extend within the user's nares and provide sealing of the nares. The flanges 73, 74 are preferably thin flexible extensions that extend substantially completely around the circumference of the prongs 64, 65. The flanges 73, 74 are preferably substantially elliptical in shape with one side (for example, side 89, which in use will abut the nasal septum of a user) of the flange extending out from each prong further than the other side of each prong. There is a recessed area 88 on each of the prongs between the flange and the shaped ends of the prongs in which preferably in use the ends of a user's nares rest.

The body part 62 is a tubular passageway in which the prong part 61 is connected at one end and a ball joint 69 at the other end. The ball joint 69 extends from the connector 63 and slots into a complementary shaped (partial sphere) socket end 70 on the body part 62. The body part 62 may also have a plurality of apertures 71 formed in it, which acts as a bias flow outlet vent. Therefore, any gases exhaled by the user through their nose will exit through the apertures 71.

A shield 75 (illustrated by the dashed line in FIG. 10) may extend over the bias vent 71 inside the body part 70 to prevent gases from the blower (gases supply 15) from interacting with the bias vent 71 and vent holes, causing noise, in use.

In a sixth embodiment as shown in FIGS. 16 and 17 a nasal cannula without a prong part is shown, but that includes a shield similar to that described above. In this embodiment a body part 90 and a ball jointed connector 91 fit together as described above. The body part 90 includes an expiratory vent shield 92 that extends down from the top wall 94 of the body part 90 and shields the outlet vent 93.

Referring back to FIGS. 10 to 13, preferably the ball joint connector 63 is angled and extends into a swivelable connector 68. The swivel connector 68 is capable in use of being connected to the inspiratory conduit 3 (see FIG. 1) that supplies gases flow to the cannula 60. The inspiratory conduit 3 may be moulded directly to the connector 68 or other connection mechanisms may be used, such as a friction fit formed between the connector 68 and the conduit 3.

In other forms of the present invention the ball joint connector 63 or the ball joint 69 may have formed in it a plurality of channels. One example of this is the embodiment of FIGS. 14 and 15. Such channels allow there to be a leak when gases flow through the connector to the cannula and prongs. The channels are therefore capable of acting as a bias flow and a separate bias flow out outlet (such as that outlet 71 described above) may not be required.

In FIGS. 14 and 15 only a body part 82 and ball jointed connector 83 are shown. The body part 82 and ball jointed connector 83 join in a manner as described above, where the substantially half sphere shaped end 84 of the body part 82 receives the substantially half sphere shaped end 85 of the connector 83. The ends 84, 85 enable a rotation between the body part 82 and connector 83. In this embodiment two channels 86, 87 are formed in the connector end 85. Two channels are shown in this embodiment but there may be only one or any number of channels. Similarly, channels may be formed in the body part end 84.

It is preferred that there is a ball and socket joint, as described above, between the body part 62 and connector 63, although other connections may be utilised, such as a flexible piece of silicone, or other appropriate connection. The connection between the cannula body and connector must be able to be flexed or rotated to allow for the inspiratory conduit 3 to be moved without causing the dislodgement of the nasal cannula 60 from the user's nares.

In the preferred form of the nasal cannula 60 of the present invention the body part 62, connector 63, ball joint 69 and swivel connector 68 are preferably made from a hard or rigid plastics material, such as polypropylene, polycarbonate or acetyl. In other forms these may be of different plastics materials to allow for increased slidability between these parts.

The prong part 61 may be supplied in various different sizes such that different sized user's may remove an existing prong part and simply attach a different sized flexible plastics prong part over the body part 62.

To provide additional comfort for the user or ensure the nasal cannula of the present invention does not fall from a user's nares, the nasal cannula 60 is preferably used in combination with a headgear strap. The strap may be similar to that shown in FIG. 1 with relation to the first form of the nasal cannula 2. In this fourth form of the nasal cannula 60 the body part 62 has headgear extensions 72, 73 that extend out from the body part 70. The extensions 72, 73 each have a channel 77, 78 formed in them that is capable of receiving an end 80, 81 of the headgear strap 79. The strap ends 80, 81 in use are threaded through apertures (preferably two) and extend into and are held in the channels 77, 78. In this form the headgear strap 79 is made from a small diameter silicon, rubber or similar type material. Therefore, when the strap ends 80, 81 are threaded through the apertures friction is created that maintains the straps within the apertures and prevents the straps from slipping from the cannula.

In other forms the ends of the headgear strap that attach to the cannula may attach to extensions (or loops) 41 on the body part 22 of the cannula shown in FIG. 6, or may attach about other appropriate areas of the cannula, for example, about the connector 23. 

What is claimed is:
 1. A mask assembly for delivering positive airway pressure to a user, the mask comprising: a first part comprising a hollow body, a first part inlet and first and second oval tubular members extending from the hollow body, the first part being flexible and formed as a single piece, the first and second oval tubular members having distal ends and proximal portions spaced from the distal ends, the distal ends being connected to the hollow body and the proximal portions comprising enlarged elliptical portions configured to seal against a user's nares in use; a rigid mask body comprising a rigid mask body inlet and a rigid mask body outlet connectable to the first part inlet so as to define an enclosed space and so as to define a longitudinal direction extending from the rigid mask body inlet at a distal end of the longitudinal direction and the proximal portions of the of the first and second oval tubular members disposed at a proximal end of the longitudinal direction, the rigid mask body comprising a first headgear extension extending from a left side of the rigid mask body and including a first headgear strap connection location and a second headgear extension extending from a right side of the rigid mask body and including a second headgear strap connection location; a headgear strap comprising first and second ends, the first end connected to the first headgear extension at the first headgear strap connection location and the second end connected to the second headgear extension at the second headgear strap connection location, the headgear strap configured to maintain the first part in a position with the first and second oval tubular members against a user's nares in use; the rigid mask body further comprising an outer surface having at least a curved portion and at least a first recessed portion recessed from the curved portion of the outer surface; a bias flow vent configured to vent a gas from the enclosed space, to an outside of the rigid mask body during use, the bias flow vent comprising a least a first plurality of apertures disposed in the first recessed portion wherein the recessed portion comprises left and right side semi-oval peripheries; and an inspiratory conduit connected to the rigid mask body and configured to deliver pressurized gases into the enclosed space for inhalation by a user in use.
 2. The mask assembly of claim 1, wherein the first plurality of apertures are arranged symmetrically on left and right sides of the rigid mask body.
 3. A mask assembly for delivering positive airway pressure to a user, the mask comprising: a first part comprising a hollow body comprising first and second oval tubular members extending from the hollow body, the first part being flexible and formed as a single piece; a rigid mask body assembly comprising first and second headgear strap connection locations and a rigid mask body inlet and being connectable to the prong part so as to define an enclosed space with the rigid mask body inlet being disposed at a distal end of longitudinal direction of the mask assembly and proximal portions of the of the first and second oval tubular members disposed at a proximal end of the longitudinal direction, the rigid mask body assembly further comprising a curved outer surface having a recessed portion recessed from the curved outer surface; a headgear strap comprising a first end and a second end, the first end connected to the first headgear strap connection location and the second end connected to the second headgear strap connection location; and a bias flow vent configured to vent a gas from the enclosed space to an outside of the rigid mask body assembly during use, the bias flow vent comprising a first plurality of apertures disposed in the recessed portion, wherein a first portion of the first plurality of apertures is arranged in a left side semi-oval arrangement and a second portion of the first plurality of apertures is arranged in a right side semi-oval arrangement.
 4. The mask assembly of claim 3, wherein the rigid mask body assembly comprises a first headgear extension extending from a left side of the rigid mask body assembly, the first headgear strap connection location being disposed on the first headgear extension, and wherein the rigid mask body assembly comprises a second headgear extension extending from a right side of the rigid mask body assembly, the second headgear strap connection location being disposed on the second headgear extension.
 5. The mask assembly of claim 4, additionally comprising an inspiratory conduit connected to the rigid mask body assembly at a conduit connection location, a first portion of the first plurality of apertures being disposed between the conduit connection location and the first headgear extension, and a second portion of the plurality of apertures being disposed between the conduit connection location and the second headgear extension.
 6. The mask assembly of claim 3, wherein the recessed portion is curved.
 7. The mask assembly of claim 3, wherein the rigid mask body assembly comprises left and right side semi-oval peripheries surrounding the recessed portion.
 8. The mask assembly of claim 7, wherein the left and right side semi-oval peripheries have rounded profiles.
 9. The mask assembly of claim 3, wherein the headgear strap comprises a tube configured to maintain the first part in a position with the first and second nasal prongs against a user's nares in use.
 10. The mask assembly of claim 3, wherein the first plurality of apertures is disposed between the first and second headgear strap connection locations.
 11. A mask assembly for delivering positive airway pressure to a user, the mask comprising: a first part comprising a hollow body and first and second oval tubular members extending from the hollow body, the first part being flexible and formed as a single piece; a rigid mask body assembly comprising first and second headgear strap connection locations and a rigid mask body inlet and being connectable to the prong part so as to define an enclosed space and with the rigid mask body inlet being disposed at a distal end of longitudinal direction of the mask assembly and the first and second oval tubular members disposed at a proximal end of the longitudinal direction; the rigid mask body assembly further comprising a curved outer surface, the curved outer surface comprising a first recessed portion; a bias flow vent configured to vent a gas from the enclosed space, to an outside of the rigid mask body assembly during use, the bias flow vent comprising at least a first plurality of apertures disposed in the recessed portion wherein the first recessed portion is disposed on a left side of the rigid mask body assembly and wherein the first recessed surface portion comprises a semi-oval shape; and a headgear strap comprising a first end and a second end, the first end connected to the first headgear strap connection location and the second end connected to the second headgear strap connection location.
 12. The mask assembly of claim 11, wherein the first recessed portion is disposed on a left side of the rigid mask body assembly.
 13. The mask assembly of claim 12, wherein the curved outer surface comprises a second recessed surface portion disposed on a right side of the rigid mask body assembly, the rigid mask body assembly further comprising a second plurality of apertures disposed in the second recessed surface portion.
 14. The mask assembly of claim 13, wherein the first and second recessed surface portions are curved.
 15. The mask assembly of claim 13, wherein the first and second recessed surface portions form a single oval shaped recess on the curved outer surface.
 16. The mask assembly of claim 11, wherein the first plurality of apertures is disposed between the first and second headgear strap connection locations. 